This invention relates broadly to flexible bearings. More specifically, it relates to bearings constructed of alternate, concentric, annular layers of elastomer and rigid material, each layer being bonded to adjacent layers; and to such bearings that are substantially free of internal, tensile stresses.
There are many uses for cylindrical bearings of the type having alternate, annular, concentric layers of elastomer and rigid material bonded together. A use of particular concern in the present invention is for supporting helicopter rotors relative to the central hub thereof. In such an application, the bearings are subjected to omni-directional, random forces. Whenever the bearing is subjected to a side force, the portion between the center of the bearing and the impressed force is under compression, while the opposite half of the bearing is under tensile stresses. Bearings of this nature perform very well under compression; but are very weak under tension and tend to fail at the bond interfaces between the elastomeric and rigid layers. This tendency is aggravated by the fact that the elastomeric layers of such bearings usually have built-in tensile stresses caused by shrinkage during cure and cooling of the elastomer when the bearing is manufactured.
Flexible bearings of the type described herein are well known and are shown in patents such as in U.S. Pat. Nos. 3,787,102 to Moran; 3,750,249 to Brandon et al.; and 2,995,907 to Orain. None of these patents, however, is concerned with the problem and solution therefor that comprises the subject matter of the present invention; i.e., means of producing such bearings that are free of internal, tensile stresses.